Method for separating platinum group element

ABSTRACT

One object of the present invention is to provide a separation process that enables the efficient separation of selenium, tellurium, and platinum group elements from a material containing selenium/tellurium and platinum group elements. In order to achieve this object, the invention provides a separation process for platinum group elements comprising: a step (A) for treating a material containing selenium/tellurium and platinum group elements with alkali, a step (B) for leaching selenium/tellurium, and a step (C) for separating the platinum group element-containing leaching residue and the selenium/tellurium leachate.

TECHNICAL FIELD

The present invention relates to a treatment process that enables theefficient separation of selenium, tellurium, and platinum group elementsfrom a material containing selenium/tellurium and platinum groupelements. Furthermore, the present invention also relates to aseparation process that enables the efficient precipitation andseparation of residual gold from a platinum group element-containingsolution obtained by treatment of the material containingselenium/tellurium and platinum group elements. A separation process ofthe present invention is ideal for a process for separating andrecovering selenium, tellurium, and platinum group elements from thereduction precipitate obtained by reduction treatment of a post-goldextraction liquid in a process for recovering noble metals from a copperelectrolysis slime.

In the present invention, a selenium/tellurium mixture refers to amixture of selenium and tellurium, and describes, for example, theprecipitate produced by neutralizing the filtrate obtained by filteringthe residue containing platinum group elements from a post-goldextraction liquid generated from a decoppered slime. Furthermore, amaterial containing selenium/tellurium and platinum group elementsrefers to a material that contains at least one of selenium andtellurium, together with platinum group elements, and the termselenium/tellurium means selenium and/or tellurium.

BACKGROUND ART

In the copper electrolysis process conducted during copper smelting,impurities that are insoluble in the electrolyte are also generated as aresidual by-product. This by-product contains significant quantities ofplatinum group elements such as Pt, Rh, Ir and Ru, as well as selenium,tellurium, gold, silver and copper. Many processes have already beenproposed for separating and recovering these metals. For example,platinum group elements are recovered from the silver anode slimeproduced during a silver refining step, and from the slime generated byadding nitric acid to this slime, leaching out the metal componentsother than gold, and then reducing the residue. Conventionally, in orderto dissolve these slimes, dissolution in aqua regia, dissolution inhydrochloric acid and hydrogen peroxide, or dissolution in hydrochloricacid under a stream of chlorine gas is conducted.

However, in the case of a material containing selenium/tellurium andplatinum group elements, in which selenium and/or tellurium coexist withthe platinum group elements, if reduction is used to generate aprecipitate, then the platinum group elements form compounds with theselenium/tellurium, which are then very difficult to dissolve in aquaregia, or hydrochloric acid and hydrogen peroxide, meaning separationand recovery becomes impossible. Hydrogen peroxide decomposes on thesurface of selenides, and is consequently effectively unable to functionas an oxidizing agent. Furthermore, a process for roasting thesecompounds to effect a vapor state separation of selenium oxide andtellurium oxide has also been proposed, although the toxicity of thesematerials leads to significant environmental problems.

A process for separating platinum group elements and selenium/telluriumcontained in a post-gold extraction liquid generated from a copperelectrolysis slime, in which the chlorine ion concentration in theliquid is maintained at no more than 1.5 mol/L, while sulfur dioxide gaswith a concentration of 8 to 12% is bubbled through the liquid at atemperature of 60 to 90° C., thus reducing and precipitating theplatinum group elements (Japanese Unexamined Patent Application, FirstPublication No. 2001-316735), and a process for obtaining the extractionresidue produced by solvent extraction of gold and platinum groupelements from the hydrochloric acid leachate obtained from a copperelectrolysis slime, and then introducing sulfur dioxide to thepost-extraction liquid to reduce and precipitate the selenium/tellurium(Japanese Patent No. 3,087,758, and Japanese Unexamined PatentApplication, First Publication No. 2001-207223) are already known.

However, in these processes, because a large number of parameters mustbe controlled during the selenium reduction, such as the hydrochloricacid concentration, the temperature, the sulfur dioxide gasconcentration, and the sulfur dioxide gas flow rate, control of theprocess is difficult, leading to a reduction in the recovery rates forthe platinum group elements and selenium/tellurium. In addition,managing the steps in the two-stage reduction treatment using sulfurdioxide is extremely difficult, and some incorporation ofselenium/tellurium or platinum group elements in the precipitates isunavoidable, meaning separation that relies solely on sulfur dioxidereduction is unsatisfactory. Furthermore, separating platinum groupelements and selenium/tellurium using solvent extraction is an expensiveprocess, and the recovery treatment required following the extraction isboth complex and time-consuming.

A process in which, instead of using treatment with hydrochloric acidand sulfur dioxide, the copper electrolysis slime is subjected to aleaching treatment in a sulfuric acidic solution under pressurizedoxygen-enriched gas (Japanese Unexamined Patent Application, FirstPublication No. Hei 5-311258), and a process in which, followingleaching of the copper electrolysis slime in a sulfuric acidic solutionunder pressurized oxygen-enriched gas, the leachate is desilvered bytreatment with chlorine ions and a sodium thiosulfate solution, andcopper is then added (Japanese Unexamined Patent Application, FirstPublication No. Hei 5-311264) have also been proposed. However, thesetypes of processes that use copper under conditions of pressurized,oxygen-enriched gas are difficult to manage and very costly, and areconsequently impractical.

Other known processes include a process in which an oxidizing agent isused to oxidize metallic selenium, and the resulting product is thenneutralized with an alkali metal carbonate or hydroxide, thus forming analkali metal selenate (Japanese Unexamined Patent Application, FirstPublication No. Sho 60-176908), a process in which a selenium-containingmaterial is reacted with an alkali metal carbonate to generate anaqueous slurry, and this slurry is then baked in an oxidizing atmosphereto produce pellets, which are then subjected to water leaching (JapaneseUnexamined Patent Application, First Publication No. Sho 56-5306), aprocess in which a tellurium-containing slime is dissolved in a mineralacid in the presence of an oxidizing agent, an alkali is then added tothe solution to precipitate and separate the copper, and the remainingsolution is then neutralized to precipitate out the tellurium (JapaneseUnexamined Patent Application, First Publication No. Sho 56-84428), anda process in which a raw material such as a copper electrolysis slime istreated with a strong acid such as hydrochloric acid, and also with anoxidizing agent such as chlorine if the raw material includes compounds,and butyl carbitol is then used as the solvent for extracting tellurium(Japanese Unexamined Patent Application, First Publication No.2000-239753). However, all of these processes have a large number ofsteps, and the recovery rates for selenium/tellurium are also low.

The present invention solves the above problems associated with theconventional technology, and has an object of providing a separationprocess which enables selenium/tellurium and platinum group elements tobe easily and efficiently separated from a material containingselenium/tellurium and platinum group elements.

Furthermore, as described above, when a separation process that relieson vaporization by roasting is applied to selenium, a large proportionof the selenium becomes hexavalent, which places a large load on thesubsequent waste water treatment.

Accordingly, the present invention provides a process for dissolving amaterial that contains both platinum group elements and selenium, whichis capable of resolving the above problems associated with conventionalprocesses, by providing a dissolution separation process that enablesefficient leaching of selenium, thus enabling separation from platinumgroup elements.

In addition, as described above, managing the steps in a two-stagereduction treatment using sulfur dioxide is extremely difficult, andsome incorporation of selenium or platinum group elements in theprecipitates is unavoidable, meaning separation that relies solely onsulfur dioxide reduction is unsatisfactory. Furthermore, processes inwhich platinum group elements are removed by solvent extraction, andsubsequently separated from selenium and/or tellurium are expensive, andthe recovery treatment required following the extraction istime-consuming. Moreover, each of these processes describes theseparation of platinum group elements and selenium that already coexistwithin a solution, and do not relate to the dissolution of a processprecipitate that contains platinum group elements and selenium and thelike.

Each of the selenium and tellurium recovery processes described above isa process in which the selenium and/or tellurium is oxidized andsolubilized, but none of these processes enables the separation ofplatinum group elements from selenium at the dissolving stage.

Furthermore, in the recovery of rhodium, which is one of the platinumgroup elements, rhodium is very susceptible to oxidation, forming a veryinsoluble rhodium oxide, and is consequently very difficult to dissolve.A process for separating rhodium from a precipitate that contains noblemetals, in which the noble metal-containing precipitate is heated with acarbon based reducing agent, and the resulting reduction product isreacted with a sulfating agent, thus forming a rhodium sulfate is known(Japanese Unexamined Patent Application, First Publication No. Hei5-125461), although this process suffers from low yields and therequirement for a high treatment temperature.

The present invention provides a solution treatment process for amaterial that contains both platinum group elements and selenium, whichis capable of resolving the above problems associated with conventionalprocesses, by providing a treatment process in which selenium isdissolved selectively and separated efficiently from platinum groupelements, and the platinum group elements remaining in the solidfraction are then dissolved and recovered.

In addition to the processes described above, known tellurium recoveryprocesses include a process in which an anode slime produced during theelectrolytic refining of copper or nickel is subjected to a wettreatment to separate the insoluble silver compounds, which aresubsequently leached with ammonia or the like to separate the silver,while the resulting residue that contains tellurium is leached withsodium carbonate (Japanese Unexamined Patent Application, FirstPublication No. 2001-11547), and a process in which thetellurium-containing filtrate generated during the solvent extraction ofgold is reduced to precipitate the selenium, and the remaining filtrateis then returned to sulfuric acid pressurized leaching conditions forleaching into the decoppered leachate (Establishment of copperprecipitate wet treatment technology, Journal of the Mining andMaterials Processing Institute of Japan, Vol. 1116, p. 484, 2000).However, processes for recovering tellurium from insoluble silvercompounds suffer from poor tellurium migration rates. Furthermore, inprocesses in which the tellurium-containing filtrate is returned topressurized leaching, the leaching rate is unsatisfactory if thetellurium is in metal form, causing an undesirable increase in theholdup volume in the process.

The present invention resolves these problems associated with theconventional treatment processes, by providing a treatment process inwhich a mixture of selenium and tellurium is alloyed with copper, thisalloy is subjected to copper electrolysis to recover electrolytic copperand generate a selenium and tellurium slime, and leaching of this copperelectrolysis slime is then used to leach out the tellurium and separatethe selenium, thus enabling the selenium and tellurium to be processedwith good efficiency.

As described above, in the copper electrolysis process of a coppersmelting process, impurities that are insoluble in the electrolyte aregenerated as a residual by-product. This by-product contains significantquantities of gold, silver, copper, platinum group elements such as Pt,Rh and Ru, as well as Se and Te. Many processes have already beenproposed for separating and recovering these noble metals. For example,a decoppered slime can be subjected to chlorination leaching, withsilver and lead being recovered from the resulting residue, and goldbeing recovered from the leachate by a solvent extraction process. Theresidual liquid following this gold extraction contains platinum groupelements, as well as Se and Te. This post-gold extraction liquid is thensubjected to a reduction treatment by introducing sulfur dioxide gasinto the system, the initial selenium precipitate that first issubjected to distillation to recover high purity selenium, and theresulting distillation residue is subjected to alkali melt treatment toeffect a separation into a selenium-containing leachate and a platinumgroup element-containing residue, whereas the tellurium that isprecipitated by continuing the introduction of sulfur dioxide gas intothe above residual liquid is subjected to alkali leaching treatment toeffect a separation into a selenium/tellurium-containing leachate and aplatinum group element-containing residue, and selenium and tellurium,and the platinum group elements are then recovered from this leachateand residue respectively.

In this type of noble metal recovery system, the gold recovery processhas conventionally employed a known solvent extraction process that usesdibutyl carbitol (DBC) (Japanese Unexamined Patent Application, FirstPublication No. Sho 57-79135). A process in which an aqueous solution ofoxalic acid is added to the extracted solution to reduce and precipitatethe gold is also known (Japanese Unexamined Patent Application, FirstPublication No. 2001-316735). However, solvent extraction processes thatuse DBC typically leave approximately 0.3% of the solvent in thepost-extraction liquid. This residual solvent can be separated bydistillation, but the small quantity of gold contained in the solventremains, and a process for efficiently removing this gold during thesubsequent steps is much sought after.

Furthermore, a process in which oxalic acid is added to the chlorinationleachate from a copper electrolysis slime, and the resulting precipitateis treated with nitric acid and melted by heating (Japanese ExaminedPatent Application, Second Publication No. Sho 64-3930), and a processin which bis(2-butoxyethyl)ether is mixed with the chlorination leachatefrom a copper electrolysis slime, the gold is extracted into the organicphase by adding ether, this organic phase is scrubbed with hydrochloricacid, and then oxalic acid is added to reduce gold (Japanese Patent No.3,087,758) are also known. However, processes in which gold isselectively reduced using oxalic acid suffer from extremely slowreaction rates in those cases where the chloride ion concentration ofthe chlorination leachate from the copper electrolysis slime is high,making the gold reduction step practically impossible.

On the other hand, a process that uses hydroxylamine hydrochloride,nitrous acid, or sulfurous acid as the reducing agent for extractinggold from gold-containing materials is also known (Japanese UnexaminedPatent Application, First Publication No. Hei 2-97626). Furthermore, aprocess in which an alkylhydroxylamine is used as a complexing agentduring the electroplating of palladium and gold and the like has alsobeen disclosed (Japanese Unexamined Patent Application, FirstPublication No. Hei 2-221392). However, the quantity of gold remainingwithin the post-gold extraction liquid generated from a decoppered slimeis minimal, and the quantities of selenium, tellurium, and platinumgroup elements are higher, and consequently even if hydroxylaminehydrochloride or an alkylhydroxylamine is added directly to thispost-gold extraction liquid, an efficient recovery of gold isimpossible.

The present invention seeks to overcome the above problems associatedwith conventional processes for recovering gold from a materialcontaining selenium/tellurium and platinum group elements generated bytreatment of the chlorination leachate from a copper electrolysis slime,by providing a process that enables the efficient separation andrecovery of gold contained within such a material containingselenium/tellurium and platinum group elements.

DISCLOSURE OF INVENTION

In order to achieve the above objectives, the present invention providesa separation process for platinum group elements comprising: a step (A)for treating a material containing selenium/tellurium and platinum groupelements with alkali, a step (B) for leaching selenium/tellurium, and astep (C) for separating the platinum group element-containing leachingresidue and the selenium/tellurium leachate.

In the above separation process, the step (A) for treating a materialcontaining selenium/tellurium and platinum group elements with alkali ispreferably an alkali melt process, wherein a flux comprising a mixtureof caustic soda and sodium nitrate is added to the material containingselenium/tellurium and platinum group elements, and the mixture ismelted by heating to a temperature exceeding the eutectic temperature ofthe flux, the step (B) for leaching selenium/tellurium is preferably awater leaching step for leaching the obtained melt with water, and thestep (C) for separating the platinum group element-containing leachingresidue and the selenium/tellurium leachate is preferably a step forconducting a solid-liquid separation using water leaching, thusseparating the mixture into a liquid fraction containing sodiumselenite, and a residue containing platinum group elements.

In the above separation process, the molar ratio between the causticsoda and the sodium nitrate is preferably within a range from 75:25 to85:15.

In the above separation process, hydrogen peroxide and hydrochloric acidare preferably added to the residue containing platinum group elementsto dissolve the platinum group elements.

In the above separation process, the material containingselenium/tellurium and platinum group elements is preferably anextraction residue process precipitate left after a solvent extractionhas been used to separate gold from the hydrochloric acid leachate froma decoppered slime.

In the above separation process, the aforementioned material containingselenium/tellurium and platinum group elements is preferably adistillation residue produced by converting a decoppered slime to aslurry by adding hydrochloric acid and hydrogen peroxide, filtering thisslurry to separate leaching residue containing primarily silver, and aleachate containing gold, platinum group elements, selenium andtellurium, subsequently adjusting the liquid characteristics of theleachate and using a solvent extraction to extract gold from theleachate, adding sulfur dioxide to the post-extraction liquid tosequentially reduce and precipitate out selenium and then tellurium, andthen heating the precipitated material containing platinum groupelements and selenium to concentrate the platinum group elements, whiledistilling and separating off selenium.

In the above separation process, the step (A) for treating a materialcontaining selenium/tellurium and platinum group elements with alkali,and the step (B) for leaching selenium/tellurium are preferablyconducted simultaneously as an alkali leaching process, wherein thematerial containing selenium/tellurium and platinum group elements isleached with alkali at high temperature, causing the selenium/telluriumto migrate into the liquid, and a solid-liquid separation is thenconducted to separate the mixture into a solid fraction containingplatinum group elements, and a liquid fraction containingselenium/tellurium.

In the above separation process, an oxidizing agent is preferably addedto the separated solid fraction generated in the solid-liquid separationunder acidic conditions using hydrochloric acid, thus dissolving theplatinum group elements.

In the above separation process, the material containingselenium/tellurium and platinum group elements is preferably leachedwith alkali at high temperature, causing the tellurium to migrate intothe liquid with the selenium, thus effecting a separation from theplatinum group elements.

In the above separation process, the material containingselenium/tellurium and platinum group elements is preferably leachedusing an alkali which concentration is at least 1 mol/L, at atemperature of at least 60° C.

In the above separation process, hydrochloric acid and either hydrogenperoxide or chlorine gas are preferably added to the solid fraction fromthe solid-liquid separation performed after the alkali leaching, thusdissolving the platinum group elements.

In the above separation process, the platinum group elements preferablycomprise one or more of rhodium, ruthenium, palladium and platinum.

In the above separation process, the material containingselenium/tellurium and platinum group elements is preferably anextraction residue process precipitate left after a solvent extractionhas been used to separate gold from the hydrochloric acid leachate froma decoppered slime.

In the above separation process, the aforementioned material containingselenium/tellurium and platinum group elements is preferably a filteredprecipitate produced by converting a decoppered slime to a slurry byadding hydrochloric acid and hydrogen peroxide, filtering this slurry toeffect a separation into a residue containing primarily silver, and aleachate containing gold, platinum group elements, selenium andtellurium, subsequently adjusting the liquid characteristics of theleachate and using a solvent extraction to separate gold from theleachate, adding sulfur dioxide to the post-extraction liquid toprecipitate either selenium or tellurium, and then subjecting thisprecipitate to solid-liquid separation.

The above separation process preferably comprises:

-   -   an alkali melt process (i), comprising a step for adding a flux        comprising a mixture of caustic soda and sodium nitrate to a        residue from a distillation treatment of a material containing        selenium/tellurium and platinum group elements, and then heating        to a temperature exceeding the melting (eutectic) temperature of        the mixture, thus dissolving the selenium/tellurium as the        aforementioned step (A) for conducting the alkali treatment, a        step for conducting water leaching as the aforementioned        step (B) for leaching selenium/tellurium, and further comprising        the aforementioned step (C) for separating the platinum group        element-containing leaching residue and the selenium/tellurium        leachate, and    -   an alkali leaching process (ii), comprising a step for leaching        a material containing selenium/tellurium and platinum group        elements with alkali at high temperature as the aforementioned        step (A) for conducting the alkali treatment and the        aforementioned step (B) for leaching selenium/tellurium, and        further comprising the aforementioned step (C) for separating        the platinum group element-containing leaching residue and the        selenium/tellurium leachate.

In the above separation process, a solution containingselenium/tellurium and platinum group elements is preferably subjectedto a reduction treatment, and the residue generated by subjecting aportion of the resulting reduction precipitate to distillation treatmentis then subjected to alkali melt treatment, while the residual reductionprecipitate is subjected to alkali leaching treatment.

In the above separation process, sulfur dioxide gas is introduced into apost-gold extraction liquid of a noble metal recovery system for acopper electrolysis slime to effect a reduction treatment, and theresidue generated by subjecting the selenium that precipitates first todistillation to effect a separation of high purity selenium ispreferably subjected to alkali melt treatment, whereas the telluriumthat precipitates next is preferably subjected to alkali leachingtreatment.

In the above separation process described above, the leachate obtainedin the water leaching of the alkali melt process is preferably recycledto the alkali leaching process, and subjected to alkali leachingtogether with the material containing selenium/tellurium and platinumgroup elements.

In the above separation process, the leachate obtained in the alkalileaching process is preferably neutralized by adding sulfuric acid orhydrochloric acid, thus precipitating selenium/tellurium.

In the above separation process, hydrochloric acid is preferably addedto the leaching residue generated in the alkali leaching process and thealkali melt process in the presence of an oxidizing agent, thusdissolving the platinum group elements.

In the above separation process, a selenium/tellurium mixture ispreferably obtained from the aforementioned selenium/tellurium leachate,and the obtained selenium/tellurium mixture is then introduced into acopper smelting and refining process to generate an alloy of seleniumand tellurium with copper, this alloy is subjected to copperelectrolysis to recover electrolytic copper, while accumulating seleniumand tellurium within the copper electrolysis slime, and this copperelectrolysis slime is then subjected to sulfuric acid oxidizingleaching, thus dissolving and separating the tellurium from the seleniumwhich remains in the leaching residue.

In the above separation process, a selenium/tellurium mixture ispreferably obtained by adding sulfuric acid or hydrochloric acid to theselenium/tellurium leachate obtained in the aforementioned alkalileaching process, thus neutralizing the leachate and precipitating theselenium/tellurium mixture, and the obtained selenium/tellurium mixtureis then introduced into a copper refining process to generate an alloyof selenium and tellurium with copper, this alloy is subjected to copperelectrolysis to recover electrolytic copper, while accumulating seleniumand tellurium within the copper electrolysis slime, and this copperelectrolysis slime is then subjected to sulfuric acid oxidizingleaching, thus dissolving and separating the tellurium from the seleniumwhich remains in the leaching residue.

In the above separation process, a selenium/tellurium mixture ispreferably obtained by adding the selenium/tellurium leachate obtainedin the aforementioned alkali melt process to the material containingselenium/tellurium and platinum group elements used in theaforementioned alkali leaching process, conducting alkali leaching, andthen adding sulfuric acid or hydrochloric acid to the resulting leachateto neutralize the leachate and precipitate the selenium/telluriummixture, and the obtained selenium/tellurium mixture is then introducedinto a copper smelting and refining process to generate an alloy ofselenium and tellurium with copper, this alloy is subjected to copperelectrolysis to recover electrolytic copper, while accumulating seleniumand tellurium within the copper electrolysis slime, and this copperelectrolysis slime is then subjected to sulfuric acid oxidizingleaching, thus dissolving and separating the tellurium from theselenium, which remains in the leaching residue.

In the above separation process, the material containingselenium/tellurium and platinum group elements is preferably a reductionprecipitate produced by introducing sulfur dioxide gas into a post-goldextraction liquid and conducting a reduction treatment.

In the above separation process, following leaching of tellurium bysulfuric acid oxidizing leaching of the copper electrolysis slime, theleachate is preferably contacted with metallic copper and the resultingcopper telluride is recovered.

In the above separation process, hydrochloric acid is preferably addedto the obtained residue containing platinum group elements in thepresence of an oxidizing agent, a solid-liquid separation is conducted,and hydroxylamine hydrochloride is then added to the filtered platinumgroup element-containing solution to selectively reduce and precipitatethe gold.

In the above separation process, alkali treatment of the materialcontaining selenium/tellurium and platinum group elements is preferablyconducted at high temperature.

In the above separation process, hydrochloric acid is preferably addedto the obtained residue containing platinum group elements in thepresence of an oxidizing agent, a solid-liquid separation is conducted,and hydroxylamine hydrochloride is then added to the filtered platinumgroup element-containing solution to selectively reduce and precipitatethe gold.

In the above separation process, the post-gold extraction liquid of anoble metal recovery system for copper electrolysis slime is preferablyused as the material containing selenium/tellurium and platinum groupelements, and sulfur dioxide gas is introduced into this post-extractionliquid to effect a reduction treatment, and the distillation residuegenerated by subjecting the selenium that precipitates first todistillation to effect a separation of high purity selenium is subjectedto alkali melt treatment to separate a residue containing platinum groupelements, whereas the tellurium that precipitates on further sulfurdioxide gas introduction into the post-extraction liquid is subjected toalkali leaching treatment to separate a residue containing platinumgroup elements, and these residues containing platinum group elementsare then combined and used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process drawing showing an outline of a solution separationprocess of the present invention, showing the steps for separating bothselenium/tellurium and platinum group elements from a materialcontaining selenium/tellurium and platinum group elements.

FIG. 2 is a process drawing showing an outline of the steps fromtreatment of a decoppered slime through to the separation process shownin FIG. 1.

FIG. 3 is a process drawing showing an outline of a separation processof the present invention, showing other steps for separating bothselenium/tellurium and platinum group elements from a materialcontaining selenium/tellurium and platinum group elements.

FIG. 4 is a process drawing showing an outline of the steps fromtreatment of a decoppered slime through to the separation process shownin FIG. 3.

FIG. 5 is a process drawing showing an outline of a separation processof the present invention, showing other steps for separating bothselenium/tellurium and platinum group elements from a materialcontaining selenium/tellurium and platinum group elements.

FIG. 6 is a process drawing showing an outline of a separation processof the present invention, showing steps for separating selenium andtellurium from a selenium/tellurium mixture.

FIG. 7 is a process drawing showing an outline of a separation processof the present invention, showing steps for separating residual goldfrom a solution containing platinum group elements.

FIG. 8A, FIG. 8B and FIG. 8C are process drawings showing outlines ofseparation processes of the present invention, showing the steps of apreferred combination of separation processes of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a more detailed description of a separation process of thepresent invention.

A first separation process of the present invention is described usingFIG. 1. As shown in the figure, the first separation process of thepresent invention is a solution treatment process for a materialcontaining selenium and platinum group elements, wherein a fluxcomprising a mixture of caustic soda and sodium nitrate is added to thematerial containing selenium and platinum group elements, the mixture ismelted by heating to a temperature exceeding the eutectic temperature ofthe flux, and the resulting melt is leached with water to effect asolid-liquid separation, thus separating the mixture into a liquidfraction containing sodium selenite, and a residue containing platinumgroup elements.

The material containing selenium and platinum group elements can use,for example, the extraction residue generated following solventextraction of gold from the hydrochloric acid leachate from a decopperedslime. This decoppered slime contains large quantities of valuablemetals such as gold, silver, platinum group elements, selenium andtellurium. The treatment process for the slime is shown in FIG. 2. Asshown in the figure, the decoppered slime is converted to a slurry byadding hydrochloric acid and hydrogen peroxide, and this slurry is thenfiltered to separate a leaching residue containing primarily silver froma leachate containing gold, platinum group elements, selenium andtellurium. Following adjustment of the liquid characteristics of theleachate, a solvent extraction is used to extract gold from theleachate. The post-extraction liquid contains the residual platinumgroup elements, selenium and tellurium. Sulfur dioxide is then added tothis post-extraction liquid to sequentially reduce and precipitate outselenium and then tellurium. Tellurium has a lower reduction potentialthan selenium, and tellurium precipitates out after the precipitation ofselenium, and thereby tellurium and selenium can be separated with eachother. Due to this reduction, platinum group elements are precipitatedtogether with selenium, and the precipitate containing platinum groupelements and selenium can be heated to concentrate the platinum groupelements and distill off the selenium. The residue followingdistillation and separation of selenium contains platinum group elementsand undistilled selenium.

Materials containing selenium and platinum group elements, such as theabove distillation residue, are combined with a flux comprising amixture of caustic soda (NaOH) and sodium nitrate (NaNO₃), and theresulting mixture is melted by heating to a temperature exceeding theeutectic temperature of the flux. This heating and melting converts theselenium to a mainly tetravalent state, generating sodium selenite(Na₂SeO₃) which subsequently dissolves. The reason for using a mixtureof caustic soda and sodium nitrate as the flux is that if only causticsoda is used, then supply of oxygen from the atmosphere is inadequate,leading to the production of sodium selenide (Na₂Se), and this sodiumselenide converts to metallic selenium and precipitates during waterleaching, meaning the platinum group elements and selenium cannot bephysically separated. Furthermore, if only sodium nitrate is used as theflux, then the oxidizing power becomes overly strong, leading to anincrease in the proportion of undesirable hexavalent selenium.

In order to enable a reduction in the melting temperature, thecomposition of the flux is preferably close to a eutectic composition.Specifically, the ratio of caustic soda: sodium nitrate is preferablywithin a range from 75:25 to 85:15 (molar ratio). Furthermore, theheating temperature must be at least the eutectic temperature of theflux (258° C.), and because the flux must have an adequate fluidity andbe capable of leaching the selenide materials, a temperature within arange from 350 to 450° C. is preferred. At temperatures within thisrange, the sodium nitrate (NaNO₃) generates oxygen but is less likely togenerate NOx, whereas if the temperature exceeds the above range, theproportion of NOx generation increases, and the oxidizing power alsostrengthens, increasing the proportion of hexavalent selenium.

Following addition of the above flux to the material containing seleniumand platinum group elements, and subsequent heating to melt the flux,the melted product is leached with water to effect a solid-liquidseparation. Sodium selenite dissolves in water, whereas the platinumgroup elements remain in the residue, and consequently by conductingwater leaching of the above melt and then filtering, the mixture can beseparated into a filtrate containing sodium selenite and a solid residuecontaining platinum group elements. The filtrate contains essentially noplatinum group elements, indicating an effective separation of seleniumfrom the platinum group elements. The platinum group elements containedwithin the solid residue are leached by adding an oxidizing agent suchas hydrogen peroxide, together with hydrochloric acid. The resultingmixture is then filtered to enable the recovery of a filtrate containingthe platinum group elements.

Accordingly, according to a first separation process of the presentinvention, the type of platinum group element selenide material that isessentially insoluble in conventional industrial wet processes, can bealmost completely dissolved, and the production of hexavalent selenium,which remains a problem in dry processes, can be suppressed to lowlevels. Furthermore, only water is required for dissolving the seleniumand leaching it from the melt, meaning the treatment costs can bereduced.

As follows is a description of a second preferred separation process ofthe present invention, using FIG. 3. As shown in FIG. 3, this secondseparation process of the present invention is a separation process inwhich the material containing selenium and platinum group elements isleached with alkali at high temperature, causing the selenium and thelike to migrate into the liquid, and a solid-liquid separation is thenconducted to separate the mixture into a solid fraction containingplatinum group elements and a liquid fraction containing selenium andthe like.

Another form of the second separation process of the present inventionfurther comprises a platinum group element dissolution and separationprocess, wherein hydrochloric acid and an oxidizing agent are added tothe separated solid fraction generated by alkali leaching, thusdissolving the platinum group elements. Furthermore, the secondseparation process also includes a process wherein the high temperaturealkali leaching causes the migration of both selenium and tellurium intothe liquid phase, thus effecting a separation from the platinum groupelements, and a process wherein the platinum group elements comprise oneor more of rhodium, ruthenium, palladium and platinum. In the presentinvention, a material containing selenium and platinum group elementsrefers to a material that contains platinum group elements such asrhodium, together with selenium and the like. Furthermore, theexpression “selenium and the like” means selenium and/or tellurium.

As described above, the material containing selenium and platinum groupelements can use, for example, the process precipitate of an extractionresidue generated following solvent extraction of gold from thehydrochloric acid leachate from a decoppered slime. This decopperedslime contains large quantities of valuable metals such as gold, silver,platinum group elements, selenium and tellurium. The treatment processfor the slime is shown in FIG. 4. As shown in the figure, the decopperedslime is converted to a slurry by adding hydrochloric acid and hydrogenperoxide, and this slurry is then filtered to effect a separation into aresidue containing primarily silver, and a leachate containing gold,platinum group elements, selenium and tellurium. Following adjustment ofthe liquid characteristics of the leachate, a solvent extraction is usedto extract gold from the leachate. The post-extraction liquid containsthe residual platinum group elements, selenium and tellurium. Sulfurdioxide is then added to this post-extraction liquid to precipitate outthe platinum group elements, selenium, and tellurium, which arerecovered as a process precipitate.

During the reduction and precipitation of selenium and tellurium fromthe above post-extraction liquid by addition of sulfur dioxide, becausetellurium has a lower reduction potential than selenium, the telluriumprecipitates out after the precipitation of selenium, and consequentlyby filtering off the selenium precipitate and then adding more sulfurdioxide to the filtrate to precipitate out the tellurium, the twoelements can be separated and recovered. During this reduction process,the platinum group elements precipitate out with both the selenium andthe tellurium. The present invention can use the selenium precipitate orthe tellurium precipitate as the target material containingselenium/tellurium and platinum group elements.

The alkali leaching of the material containing selenium and platinumgroup elements is typically conducted under an alkali concentration ofat least 1 mol/L, and concentrations within a range from 5 mol/L to 8mol/L are preferred. By ensuring that the alkali concentration is atleast 1 mol/L, a strong alkali environment of at least pH 14 isachieved, which causes a reduction in the oxidation-reduction potentialof selenium and tellurium, meaning selenium and tellurium can bedissolved into the alkali solution at normal pressure, without the needto use an oxidizing agent. Because the progress of this selenium andtellurium dissolution reaction is slow at room temperature, the leachingis typically conducted at a temperature of at least 60° C., andpreferably at a temperature of approximately 80° C.

The alkali leaching causes the selenium and tellurium to be dissolvedinto the alkali solution, where they are dispersed in colloid form. Incontrast, platinum group elements such as rhodium and palladium are notdissolved and remain in the solid phase. Filtering the resulting mixtureenables a separation into a dispersion containing selenium and/ortellurium, and a solid fraction containing the platinum group elements.

Following the above solid-liquid separation, an oxidizing agent such ashydrogen peroxide and hydrochloric acid are added to the filtered solidfraction, thus dissolving the platinum group elements such as platinum,palladium, rhodium and ruthenium. The platinum group elements areoxidized by hydrogen peroxide, and then form chloride complexes with thechlorine ions, enabling them to be stabilized and dissolved in theliquid phase. The hydrogen peroxide is added in the quantity required toconvert the platinum group elements into ions with stable oxidationnumbers, namely, the quantity required to convert platinum to atetravalent form, palladium to a bivalent form, and rhodium andruthenium to trivalent forms. The quantity of hydrochloric acid used issufficient to generate PtCl₆ ⁻, PdCl₄ ⁻, RhCl₆ ³⁻, and RuCl₆ ³⁻respectively, as well as leave at least 2 mol/L free hydrochloric acid.The reaction temperature is typically at least 60° C. in order toaccelerate the reaction, and is typically no more than 80° C. in orderto suppress decomposition of the hydrogen peroxide, and a temperature ofapproximately 70° C. is preferred. This dissolution treatment enables ahydrochloric acid solution containing dissolved platinum, palladium,rhodium and ruthenium to be obtained.

According to the second separation process of the present invention, bysubjecting a material containing selenium and platinum group elements toalkali leaching at a treatment temperature within a range from 60 to 80°C., selenium and tellurium can be dissolved and separated from theplatinum group elements at normal pressure, and without the use of anoxidizing agent. Accordingly, selenium and tellurium can be separatedeasily from a process precipitate containing selenium and tellurium aswell as platinum group elements, and the platinum group elements can beselectively recovered with a yield of 95% or higher. Moreover, becausethe platinum group elements are not oxidized during this alkalileaching, highly insoluble oxides such as rhodium oxide and rutheniumoxide are not produced, meaning the platinum group elements can besubsequently easily dissolved. The platinum group elements in the alkalileaching residue can be subsequently oxidized in the presence ofhydrochloric acid, thus forming chloride complexes, and generating aplatinum group element solution. The dissolved selenium and telluriumare dispersed in colloid form, and can be precipitated as metals byneutralizing the leachate, and consequently these two metals can also berecovered with ease. Conventional alkali leaching processes that use anoxidizing agent require the leaching to be conducted under pressurizedconditions, and because they generate sodium selenate and/or sodiumselenite, subsequent recovery of the selenium is time-consuming. Incontrast, the treatment process of the present invention enables thedissolution of selenium and tellurium, and enables the separation ofthese elements from the platinum group elements to be conducted atnormal pressure, without the use of an oxidizing agent, meaning processcontrol and the recovery treatment are much easier.

Next is a description of a third preferred separation process of thepresent invention, using FIG. 5. As shown in the figure, this thirdseparation process of the present invention is a process for separatingboth selenium and platinum group elements from a material containingselenium/tellurium and platinum group elements, which comprises analkali leaching process (ii) for subjecting a material containingselenium/tellurium and platinum group elements to alkali treatment athigh temperature, thus separating the material into a leachatecontaining selenium/tellurium and a leaching residue containing platinumgroup elements, and an alkali melt process (i) for adding a mixture ofcaustic soda and sodium nitrate to a residue from a distillationtreatment of a material containing selenium and platinum group elements,subsequently heating to a temperature exceeding the melting (eutectic)temperature of the mixture, thus dissolving the selenium/tellurium, andthen performing water leaching to separate the mixture into a leachatecontaining selenium/tellurium and a leaching residue containing platinumgroup elements.

[Material Containing Selenium/Tellurium and Platinum Group Elements]

As described above, the material containing selenium/tellurium andplatinum group elements can use, for example, the reduction processprecipitate of an extraction residue generated following solventextraction of gold from the hydrochloric acid leachate from a decopperedslime. This decoppered slime contains large quantities of valuablemetals such as gold, silver, platinum group elements, selenium andtellurium. Specifically, the material containing selenium/tellurium andplatinum group elements is obtained by treating the decoppered slime inthe following manner. First, the decoppered slime is converted to aslurry by adding hydrochloric acid and hydrogen peroxide, and thisslurry is then filtered to separate a residue containing primarilysilver from a leachate containing gold, platinum group elements,selenium and tellurium. Following adjustment of the liquidcharacteristics of the leachate, a solvent extraction using DBC or thelike is used to extract gold from the leachate. The post-extractionliquid contains the residual platinum group elements, as well asselenium and tellurium. Sulfur dioxide, and more specifically sulfurdioxide gas, is then introduced into this post-extraction liquid in aquantity sufficient to retain the selenium concentration in the liquidat a value of 3 g/L or higher, thus reducing and precipitating theselenium, and effecting a separation from the remaining post-extractionliquid. Further sulfur dioxide is then introduced into the remainingpost-extraction liquid from which the selenium has been separated, thusreducing and precipitating out the residual selenium, together with thetellurium, which can be separated by subsequent filtration.

The third separation process of the present invention can use thepost-gold extraction liquid described above as a liquid containingselenium/tellurium and platinum group elements. Furthermore, theseparation process can use the reduction precipitate from the abovepost-gold extraction liquid, or the distillation residue generated uponsubsequent distillation, as the material containing selenium/telluriumand platinum group elements. In addition, waste water from a platingfactory, or other solutions containing selenium/tellurium and platinumgroup elements such as smelting waste water can also be used as thematerial containing selenium/tellurium and platinum group liquid.

In the reduction treatment of the above post-gold extraction liquid,when the selenium and the tellurium are reduced and precipitated,because tellurium has a lower reduction potential than selenium, thetellurium precipitates after the precipitation of selenium, andconsequently by filtering off the selenium precipitate and then addingmore sulfur dioxide to the filtrate to precipitate the tellurium, thetwo elements can be separated and recovered. During this reductionprocess, the platinum group elements precipitate together with both theselenium and the tellurium.

The materials containing selenium/tellurium and platinum group elementsobtained in this manner are treated in a subsequent alkali leachingprocess and an alkali melt process. In this case, the selenium thatprecipitates first on reduction of the extraction residue is preferablysubjected to distillation to enable the recovery of high purityselenium, and the residue (distillation residue) is subjected to alkalimelt treatment, whereas the tellurium that is precipitated afterwards ispreferably subjected to alkali leaching treatment. The distillationresidue includes compounds such as palladium selenide, and is stable,and consequently selenium dissolution cannot be achieved by alkalileaching. By subjecting the distillation residue to alkali melttreatment, the selenium can be processed efficiently. In contrast, therhodium and ruthenium incorporated in the tellurium precipitate is of arelatively higher content than that contained in the seleniumprecipitate, and consequently if the tellurium precipitate is subjectedto alkali melting, it is prone to forming insoluble oxides, making thesubsequent hydrochloric acid leaching step difficult. Accordingly, thetellurium precipitate preferably undergoes alkali leaching treatment.

[Alkali Melt Process]

The above material containing selenium/tellurium and platinum groupelements, such as the selenium precipitate or the aforementionedselenium distillation residue undergo alkali melt treatment. In thisalkali melt treatment, a flux comprising a mixture of caustic soda(NaOH) and sodium nitrate (NaNO₃) is added to the selenium precipitateor the selenium distillation residue, and the resulting mixture ismelted by heating to a temperature exceeding the melting point (eutectictemperature) of the flux. This heating and melting converts the seleniumto a mainly tetravalent state, generating sodium selenite (Na₂SeO₃)which subsequently dissolves. The reason for using a mixture of causticsoda and sodium nitrate as the flux is that if only caustic soda isused, then supply of oxygen from the atmosphere is inadequate, leadingto the production of sodium selenide (Na₂Se), and this sodium selenideconverts to metallic selenium and precipitates during water leaching,meaning the platinum group elements and selenium cannot be physicallyseparated. Furthermore, if only sodium nitrate is used as the flux, thenthe oxidizing power becomes overly strong, leading to an increase in theproportion of undesirable hexavalent selenium.

In order to reduce the melting temperature, the composition of the fluxis preferably close to a eutectic composition. Specifically, the ratioof caustic soda: sodium nitrate is preferably within a range from 75:25to 85:15 (molar ratio). Furthermore, the heating temperature must be atleast the eutectic temperature of the flux (258° C.), and because theflux must have an adequate fluidity and be capable of leaching theselenide materials, a heating temperature within a range from 350 to450° C. is preferred. At temperatures within this range, the sodiumnitrate (NaNO₃) generates oxygen but is less likely to generate NOx,whereas if the temperature exceeds the above range, the proportion ofNOx generation increases, and the oxidizing power also strengthens,increasing the proportion of hexavalent selenium.

Following addition of the above flux to the material containing seleniumand platinum group elements and subsequent heating to melt the flux, themelted product is leached with water to effect a solid-liquidseparation. Sodium selenite dissolves in water, whereas the platinumgroup elements remain in the residue, and consequently by conductingwater leaching of the above melt and then filtering, the mixture can beseparated into a filtrate containing sodium selenite and a solid residuecontaining platinum group elements. The filtrate contains essentially noplatinum group elements, indicating an effective separation of seleniumfrom the platinum group elements. The platinum group elements containedin the solid residue are dissolved by adding hydrochloric acid, togetherwith an oxidizing agent such as hydrogen peroxide. The resulting mixtureis then filtered to enable the recovery of a filtrate containing theplatinum group elements.

[Alkali Leaching Process]

The material containing selenium/tellurium and platinum group elementsundergoes alkali leaching treatment. Alkali leaching is typicallyconducted under an alkali concentration of at least 1 mol/L, andconcentrations within a range from 5 mol/L to 8 mol/L are preferred. Byensuring that the alkali concentration is at least 1 mol/L, a strongalkali environment of at least pH 14 is achieved, which causes areduction in the oxidation-reduction potential of selenium andtellurium, meaning selenium and tellurium can be dissolved into thealkali solution at normal pressure, without the need to use an oxidizingagent. Because the progress of this selenium and tellurium dissolutionreaction is slow at room temperature, the leaching is typicallyconducted at a temperature of at least 60° C., and preferably at atemperature of approximately 80° C.

The alkali leaching causes the selenium and tellurium to be dissolvedinto the alkali solution, where they are dispersed in colloid form. Incontrast, platinum group elements such as rhodium and palladium are notdissolved and remain in the solid phase. Filtering the resulting mixtureenables a separation into a leachate containing selenium and/ortellurium, and a solid fraction containing the platinum group elements.

Following the above solid-liquid separation, if sulfuric acid orhydrochloric acid is added to the filtrate containing selenium/telluriumto effect a neutralization, a black colored precipitate of metallicselenium and/or metallic tellurium develops, and the color of thesolution gradually lightens from a deep purple color, until the liquidbecomes transparent at around pH 7. The assay of this seleniumprecipitate and/or tellurium precipitate is typically 99% or better,enabling the recovery of high quality metallic selenium and/or metallictellurium. If nitric acid is used instead of the sulfuric acid orhydrochloric acid, the oxidizing power of the nitric acid causes theselenium/tellurium to oxidize and dissolve, meaning precipitation is notpossible. Furthermore, the liquid temperature is preferably from 60 to80° C. If neutralization is conducted at a liquid temperature withinthis range, metallic selenium with good filterability can be obtained.

An oxidizing agent such as hydrogen peroxide, and hydrochloric acid areadded to the filtered solid fraction containing the platinum groupelements, thus dissolving the platinum group elements such as platinum,palladium, rhodium and ruthenium. The platinum group elements areoxidized by hydrogen peroxide, and then form chloride complexes with thechloride ions, enabling them to be stabilized and dissolved in theliquid phase. The hydrogen peroxide is added in the quantity required toconvert the platinum group elements into ions with stable oxidationnumbers, namely, the quantity required to convert platinum to atetravalent form, palladium to a bivalent form, and rhodium andruthenium to trivalent forms. The quantity of hydrochloric acid used ispreferably sufficient to generate PtCl₆ ⁻, PdCl₄ ⁻, RhCl₆ ³⁻, and RuCl₆³⁻ respectively, as well as leave at least 2 mol/L free hydrochloricacid. The reaction temperature is typically at least 60° C. in order toaccelerate the reaction, and is typically no more than 80° C. in orderto suppress decomposition of the hydrogen peroxide, and a temperature ofapproximately 70° C. is preferred. This dissolution treatment enables ahydrochloric acid solution containing dissolved platinum, palladium,rhodium and ruthenium to be obtained.

As described above, by subjecting a material containing selenium andplatinum group elements to alkali leaching at a treatment temperaturewithin a range from 60 to 80° C., selenium and tellurium can bedissolved and separated from the platinum group elements at normalpressure, and without the use of an oxidizing agent. Accordingly,selenium and tellurium can be separated easily from a processprecipitate containing selenium and tellurium as well as platinum groupelements, and the platinum group elements can be selectively recoveredwith a yield of 95% or higher. Moreover, because the platinum groupelements are not oxidized during this alkali leaching, highly insolubleoxides such as rhodium oxide and ruthenium oxide are not produced,meaning the platinum group elements can be subsequently easilydissolved. The platinum group elements in the leaching residue can berecovered by oxidizing in the presence of hydrochloric acid, thusforming chloride complexes, and generating a platinum group elementsolution. The dissolved selenium and tellurium are dispersed in colloidform, and can be precipitated as metals by neutralizing the leachatewith either sulfuric acid or hydrochloric acid, and consequently thesetwo metals can also be recovered with ease. Conventional alkali leachingprocesses that use an oxidizing agent require the leaching to beconducted under pressurized conditions, and generate sodium selenateand/or sodium selenite, and the presence of hexavalent selenium meansthe removal of selenium from waste water is difficult. In contrast, thetreatment process of the present invention enables the dissolution ofselenium and tellurium, and the separation of these elements from theplatinum group elements to be conducted at normal pressure, without theuse of an oxidizing agent, meaning process control and the recoverytreatment can be completed without the generation of hexavalentselenium.

As described above, in the alkali melt process, the selenium and/ortellurium is dissolved in the water in the form of sodium selenite orsodium tellurite, and is subsequently separated from the leachingresidue that contains the platinum group elements. However, theseparated water leachate may still contain small residual quantities ofplatinum group elements in addition to the selenium/tellurium, andconsequently the water leachate is preferably recycled into the abovealkali leaching process, and subjected to alkali leaching together withthe material containing selenium/tellurium and platinum group elements.This recycling treatment concentrates the selenium/tellurium.

On the other hand, the leaching residue containing platinum groupelements obtained in the alkali melt process is combined with anoxidizing agent such as hydrogen peroxide together with hydrochloricacid, in the same manner as the residue from the alkali leachingprocess, thus dissolving the platinum group elements such as platinum,palladium, rhodium and ruthenium. The platinum group elements areoxidized by hydrogen peroxide, and then form chloride complexes with thechlorine ions, enabling them to be stably dissolved in the liquid phase.This dissolution treatment enables a hydrochloric acid solutioncontaining dissolved platinum, palladium, rhodium and ruthenium to beobtained. This chlorination treatment is preferably conducted togetherwith the leaching residue obtained in the alkali leaching process.

According to the third separation process of the present invention, thematerial containing selenium/tellurium and platinum group elements istreated using a combination of an alkali leaching process, in whichalkali leaching is conducted at high temperature, and an alkali meltprocess, in which a mixture of caustic soda and sodium nitrate is added,and the mixture is melted by heating to a temperature exceeding themelting (eutectic) temperature to dissolve the selenium/tellurium, andas a result, the selenium/tellurium and the platinum group elements canbe concentrated and almost entirely recovered, enabling aneasily-refined hydrochloric acid solution to be supplied to a subsequentrefining step, and enabling platinum group elements andselenium/tellurium to be separated simply, efficiently, and at low cost,from a material containing selenium/tellurium and platinum groupelements.

As follows is a description of a fourth preferred separation process ofthe present invention, using FIG. 6.

The fourth separation process described below is a treatment process forselenium/tellurium in which a selenium/tellurium mixture is introducedinto a copper smelting and refining process to generate an alloy ofselenium and tellurium with copper, this alloy is subjected to copperelectrolysis to recover electrolytic copper, while accumulating seleniumand tellurium within the copper electrolysis slime, and this copperelectrolysis slime is then subjected to sulfuric acid oxidizing leachingto dissolve the tellurium, thus enabling the tellurium to be separatedfrom the selenium which remains in the leaching residue.

More specifically, as shown by the treatment process shown in FIG. 6, anaforementioned material containing selenium/tellurium and platinum groupelements is used as the selenium/tellurium mixture, and as describedabove, this material first passes through the alkali leaching process,in which the mixture is subjected to alkali leaching at high temperatureto effect a separation into a leachate containing selenium/tellurium anda leaching residue containing platinum group elements. Sulfuric acid orhydrochloric acid is then added to the leachate to neutralize theleachate and precipitate the selenium/tellurium mixture, and thismixture is introduced into the copper refining process to generate analloy of selenium and tellurium with copper. This alloy is subjected tocopper electrolysis to recover electrolytic copper, while accumulatingselenium and tellurium within the copper electrolysis slime, and thiscopper electrolysis slime is then subjected to sulfuric acid oxidizingleaching to elute the tellurium, thus enabling the tellurium to beseparated from the selenium, which remains in the leaching residue.

[Selenium/Tellurium Mixture]

In the fourth separation process of the present invention, theselenium/tellurium mixture can use a treated material containingselenium/tellurium and platinum group elements from a copper process.Specifically, the type of material containing selenium/tellurium andplatinum group elements that was used in the first through thirdseparation processes can be used.

This material containing selenium/tellurium and platinum group elementsis then treated in the alkali leaching process and alkali melt processdescribed below. As was the case in the above separation processes, inthe fourth separation process, the selenium that precipitates first onreduction of the post-extraction liquid is preferably subjected todistillation to enable the recovery of high purity selenium, and theresidue (distillation residue) is subjected to alkali melt treatment,whereas the tellurium that is precipitated afterwards is preferablysubjected to alkali leaching treatment. The distillation residueincludes compounds such as palladium selenide, and is stable, andconsequently selenium dissolution cannot be achieved by alkali leaching.By subjecting the distillation residue to alkali melt treatment, theselenium can be processed efficiently. In contrast, the rhodium andruthenium incorporated in the tellurium precipitate is of a relativelyhigher content than that contained in the selenium precipitate, andconsequently if the tellurium precipitate is subjected to alkalimelting, it is prone to forming insoluble oxides, making the subsequenthydrochloric acid leaching step difficult. Accordingly, the telluriumprecipitate preferably undergoes alkali leaching treatment.

[Alkali Leaching Process]

As described in the separation process above, the material containingselenium/tellurium and platinum group elements undergoes alkali leachingtreatment. Alkali leaching is typically conducted under an alkaliconcentration of at least 1 mol/L, and concentrations within a rangefrom 5 mol/L to 8 mol/L are preferred. By ensuring that the alkaliconcentration is at least 1 mol/L, a strong alkali environment of atleast pH 14 is achieved, which causes a reduction in theoxidation-reduction potential of selenium and tellurium, meaningselenium and tellurium can be dissolved into the alkali solution atnormal pressure, without the need to use an oxidizing agent. Because theprogress of this selenium and tellurium dissolution reaction is slow atroom temperature, the leaching is typically conducted at a temperatureof at least 60° C., and preferably at a temperature of approximately 80°C.

The alkali leaching causes the selenium and tellurium to be dissolvedinto the alkali solution, where they are dispersed in colloid form. Incontrast, platinum group elements such as rhodium and palladium are notdissolved and remain in the solid phase. Filtering the resulting mixtureenables a separation into a leachate containing selenium and/ortellurium, and a solid fraction containing the platinum group elements.

The above alkali leaching may also be conducted on a combination of thematerial containing selenium/tellurium and platinum group elements, andthe leachate obtained by subjecting the residue from the aforementioneddistillation treatment to alkali melt treatment. The seleniumprecipitate obtained by reduction treatment of the material containingselenium/tellurium and platinum group elements, or the residue obtainedfrom distillation treatment of this reduced selenium precipitate iscombined with a flux comprising a mixture of caustic soda (NaOH) andsodium nitrate (NaNO₃), and the resulting mixture is melted by heatingto a temperature exceeding the melting point (eutectic temperature) ofthe flux. This heating and melting converts the selenium to a mainlytetravalent state, generating sodium selenite (Na₂SeO₃) whichsubsequently dissolves. This alkali melt treatment causes theselenium/tellurium to dissolve, and water leaching is then used toseparate the mixture into a leachate containing the selenium/tellurium,and a leaching residue containing the platinum group elements. Thisleachate can be added to the alkali leaching process of materialscontaining selenium/tellurium and platinum group elements, and subjectedto alkali leaching, as described above. Using the leachate obtained fromthis alkali melt process enables the overall selenium/tellurium recoveryrate for the entire treatment process to be improved.

Following the above solid-liquid separation of the alkali leaching, ifsulfuric acid or hydrochloric acid is added to the filtrate containingselenium/tellurium to effect a neutralization, a black coloredprecipitate of metallic selenium and/or metallic tellurium develops, andthe color of the solution gradually lightens from a deep purple color,until the liquid becomes transparent at around pH 7. By conducting asolid-liquid separation, a mixture of metallic tellurium and metallicselenium can be recovered. The assay of this selenium/tellurium mixtureis typically 99% or better, enabling the recovery of high qualitymetallic selenium and/or metallic tellurium. If nitric acid is usedinstead of the sulfuric acid or hydrochloric acid, the oxidizing powerof the nitric acid causes the selenium/tellurium to oxidize anddissolve, meaning precipitation is not possible. The liquid temperatureis preferably from 60 to 80° C. If neutralization is conducted at aliquid temperature within this range, a selenium/tellurium mixture withgood filterability can be obtained.

In the fourth separation process of the present invention, the aboveselenium/tellurium mixture is introduced into the copper smelting andrefining process to generate an alloy of selenium and tellurium withcopper, and this alloyed copper (crude copper) then undergoeselectrolysis to recover electrolytic copper, while the selenium andtellurium are accumulated within the copper electrolysis slime, togetherwith the other insoluble components. The copper electrolysis can beconducted under normal copper electrolysis conditions. The copperelectrolysis yields high purity electrolytic copper, while the seleniumand tellurium form a copper electrolysis slime with the other insolublecomponents that were incorporated within the crude copper. By subjectingthis copper electrolysis slime to air oxidation in sulfuric acid andconducting a leaching treatment (copper removal leaching), the majorityof the copper and tellurium contained within the slime can be dissolved.Sulfuric acid electrolyte can be used as the sulfuric acid for thisstep. Bringing the dissolved copper leachate containing tellurium intocontact with metallic copper forms copper telluride, meaning thetellurium can be recovered as copper telluride. From an industrialviewpoint, the dissolved copper leachate containing tellurium ispreferably passed through a column packed with copper chip to recoverthe copper telluride. On the other hand, the selenium remains in theleaching residue (decoppered slime), and consequently this copperremoval leaching can be used to separate selenium and tellurium.

Following the above copper removal leaching, the leachate containingcopper and selenium is retuned to the copper electrolysis step, and thecopper is recovered as electrolytic copper. As described above, theselenium accumulates in the copper electrolysis slime, and consequentlyby repeating the sulfuric acid oxidizing leaching (copper removalleaching) of the copper electrolysis slime, the selenium becomesconcentrated within the decoppered slime. Furthermore, this decopperedslime also contains large quantities of noble metals such as gold,silver, platinum group elements, and lead, and consequently byconducting a chlorination leaching of the decoppered slime byintroducing an oxidizing agent such as hydrogen peroxide or chlorine gastogether with hydrochloric acid or the like, these noble metals can bedissolved, and then recovered by employing treatment processes suited torecovery of each of the noble metal elements.

In one example of a process for recovering a noble metal, the silver andlead contained in the slime are converted to insoluble chlorides throughthe above chlorination leaching, while the gold, platinum groupelements, selenium and tellurium are dissolved in the leachate, asolid-liquid separation is then conducted to effect a separation into aleaching filtrate containing gold and platinum group elements and thelike, and a leaching filtered residue containing silver and lead, andthe treatment process described above is then used to separate andrecover silver and lead from this silver and lead-containing residue.Furthermore, a solvent extraction can be used to extract gold from theleaching filtrate containing tellurium and platinum group elements andthe like, and a subsequent reduction then used to recover the gold,while the post-extraction liquid can be subjected to distillationtreatment, the selenium and the tellurium reduced, and the resultingreduction precipitate used to repeat the treatment of the presentinvention, thus enabling the selenium and tellurium to be concentrated,and recovered with a good level of efficiency.

According to the fourth separation process of the present invention, aselenium/tellurium mixture is introduced into a copper refining processto generate an alloy of selenium and tellurium with copper, and thiscopper alloy is subjected to electrolysis to recover high purityelectrolytic copper, while the selenium and tellurium are accumulated inthe copper electrolysis slime, and consequently by subjecting thiscopper electrolysis slime to sulfuric acid oxidizing leaching (copperremoval leaching), the tellurium can be dissolved into the solution andseparated from the selenium, and the dissolved tellurium can beseparated and recovered through contact with metallic copper to generatecopper telluride. Furthermore, the selenium that remains in the copperleaching residue can be separated and recovered by reduction treatment,following the completion of noble metal recovery processes such as agold extraction process.

As follows is a description of a fifth preferred separation process ofthe present invention, using FIG. 7. As shown in FIG. 7, the fifthseparation process is a treatment process for separating gold from asolution containing platinum group elements, wherein a materialcontaining selenium/tellurium and platinum group elements is subjectedto alkali treatment to effect a separation into a leachate containingselenium/tellurium and a residue containing platinum group elements,hydrochloric acid is added to this residue containing the platinum groupelements in the presence of an oxidizing agent, a solid-liquidseparation is conducted, and hydroxylamine hydrochloride is then addedto the filtered solution containing the platinum group elements toselectively reduce and precipitate gold.

Even in this fifth separation process of the present invention, amaterial containing selenium/tellurium and platinum group elementsobtained in a copper smelting process can be used, in a similar mannerto that described in the first separation process.

[Alkali Treatment]

The material containing selenium/tellurium and platinum group elementsundergoes alkali treatment, and is separated into a leachate containingselenium/tellurium and a residue containing platinum group elements. Asdescribed above, this alkali treatment can involve either an alkalileaching process or an alkali melt process, or may include bothprocesses. In those cases where both the alkali leaching process and thealkali melt process are carried out, the selenium that precipitatesfirst on reduction of the aforementioned post-extraction liquid ispreferably subjected to distillation to enable the recovery of highpurity selenium, and the residue (distillation residue) is subjected toalkali melt treatment, whereas the tellurium that is precipitatedafterwards is preferably subjected to alkali leaching treatment. Thedistillation residue includes compounds such as palladium selenide, andis stable, and consequently selenium dissolution cannot be achieved byalkali leaching. By subjecting the distillation residue to alkali melttreatment, the selenium can be processed efficiently. In contrast, therhodium and ruthenium incorporated in the tellurium precipitate is of arelatively higher content than that contained in the seleniumprecipitate, and consequently if the tellurium precipitate is subjectedto alkali melting, it is prone to forming insoluble oxides, making thesubsequent hydrochloric acid leaching step difficult. Accordingly, thetellurium precipitate preferably undergoes alkali leaching treatment.

[Alkali Melting]

In the alkali leaching treatment, the selenium precipitate obtained byreduction treatment of the material containing selenium/tellurium andplatinum group elements, or the residue obtained from distillationtreatment of this reduced selenium precipitate is combined with a fluxcomprising a mixture of caustic soda (NaOH) and sodium nitrate (NaNO₃),and the resulting mixture is melted by heating to a temperatureexceeding the melting point (eutectic temperature) of the flux. Thisheating and melting converts the selenium to a mainly tetravalent state,generating sodium selenite (Na₂SeO₃) which subsequently dissolves. Thisalkali melt treatment causes the selenium/tellurium to dissolve, andwater leaching is then used to separate the mixture into a leachatecontaining the selenium/tellurium, and a leaching residue containing theplatinum group elements. This leachate can be added to the alkalileaching process of materials containing selenium/tellurium and platinumgroup elements, and subjected to alkali leaching, as described above.Using the leachate obtained from this alkali melt process enables theoverall selenium/tellurium recovery rate for the entire treatmentprocess to be improved.

[Alkali Leaching]

Alkali leaching treatment of the material containing selenium/telluriumand platinum group elements is typically conducted under an alkaliconcentration of at least 1 mol/L, and concentrations within a rangefrom 5 mol/L to 8 mol/L are preferred. By ensuring that the alkaliconcentration is at least 1 mol/L, a strong alkali environment of atleast pH 14 is achieved, which causes a reduction in theoxidation-reduction potential of selenium and tellurium, meaningselenium and tellurium can be dissolved into the alkali solution atnormal pressure, without the need to use an oxidizing agent. Because theprogress of this selenium and tellurium dissolution reaction is slow atroom temperature, the leaching is typically conducted at a temperatureof at least 60° C., and preferably at a temperature of approximately 80°C.

The alkali leaching causes the selenium and tellurium to be dissolvedinto the alkali solution, where they are dispersed in colloid form. Incontrast, platinum group elements such as rhodium and palladium are notdissolved and remain in the solid phase. Filtering the resulting mixtureenables a separation into a leachate containing selenium and/ortellurium, and a solid fraction containing the platinum group elements.

In the process of the present invention, hydroxylamine hydrochloride isadded to the solution containing the platinum group elements obtained inthe alkali treatment described above to selectively reduce andprecipitate gold. Provided hydroxylamine hydrochloride is used as thereducing agent, gold can be selectively reduced and precipitated out,even if the platinum group element solution is hydrochloric acidic. Thequantity of hydroxylamine hydrochloride added is typically within arange from 1.3 to 1.6 equivalents relative to the quantity of gold. Ifthis quantity is less than 1.3 equivalents, then the reduction of thegold is unsatisfactory, whereas if the quantity exceeds 1.6 equivalents,then the platinum group elements, and particularly palladium, arereduced together with the gold, meaning the gold cannot be selectivelyrecovered. The reduction temperature is preferably at least 60° C. Attemperatures less than 60° C., the reduction reaction is slow, makingthe process industrially unsuitable.

Hence, according to this separation process of the present invention,residual gold contained in a platinum group element solution obtained bytreating a material containing selenium/tellurium and platinum groupelements can be precipitated and separated with a high level ofefficiency. Accordingly, the separation process of the present inventionis ideal for use in a process for recovering noble metals from a copperelectrolysis slime, and is used for removing gold during the step forseparating and recovering selenium/tellurium and platinum group elementsfrom the reduction precipitate generated during reduction of a post-goldextraction liquid.

FIG. 8A, FIG. 8B and FIG. 8C are process drawings showing outlines ofthe separation processes of the present invention, showing the stepswithin a preferred combination of the first through fifth separationprocesses of the present invention.

As shown in FIG. 8, it is evident that by combining the preferredseparation processes described above, selenium, tellurium, platinumgroup elements, and gold and the like can be easily separated from adecoppered slime, and more particularly from a material containingselenium/tellurium and platinum group elements that has been separatedfrom a decoppered slime.

Specifically, the first separation process corresponds substantially tothe steps in FIG. 8B from NaOH melting through to water leaching andfiltration, and the second separation process corresponds substantiallyto the steps from NaOH elution through to filtration. Furthermore, thesteps from NaOH elution through to filtration, and the steps from NaOHmelting through to water leaching and filtration also correspondsubstantially to the third separation process. The fourth separationprocess corresponds to the steps from copper smelting through totellurium removal in FIG. 8C. The fifth separation process correspondssubstantially to the steps in FIG. 8B from NaOH leaching through tofiltration, and the steps for subjecting the leachate containingselenium/tellurium, obtained in the steps from NaOH melting through towater leaching and filtration, to chlorination, filtration, andsubsequent gold removal and filtration.

As follows, a series of examples and comparative examples of the presentinvention are described. Unless stated otherwise, the units % refer to %by weight (wt %) values.

EXAMPLE 1

Using 20 g of a platinum group element-containing material, comprisingpalladium selenide as the primary component, as a raw material, 21.7 gof caustic soda and 11.5 g of sodium nitrate were mixed with the rawmaterial, and the mixture was heated for 2 hours at 400° C., forming amelt. Following cooling of the melt, 500 ml of water was added, and themixture was stirred for one hour and then filtered. 97.4% of theselenium from the above raw material had been leached into the filtrate.Furthermore, platinum and palladium were not detected in the filtrate.The quantity of hexavalent selenium in the filtrate was less than 10%.Meanwhile, the filtered residue was repulped with 3N hydrochloric acid,and was then oxidized with hydrogen peroxide. As a result, 95% of thepalladium and 99% or greater of the platinum were leached into thesolution.

EXAMPLE 2

With the exception of using 20.3 g of caustic soda and 14.4 g of sodiumnitrate, the same method as the example 1 was used to heat and melt 20 gof the platinum group element-containing material comprising palladiumselenide as the primary component, and then subject this melt to waterleaching and filtering. The leaching rate of selenium into the filtratewas 98.2%. Platinum and palladium were not detected in the filtrate.Furthermore, the proportion of hexavalent selenium in the filtrate wasless than 10%. Meanwhile, when the filtered residue was repulped with 3Nhydrochloric acid, and then oxidized with hydrogen peroxide, theleaching rate of palladium into the solution was 95%, and the leachingrate for platinum was 99% or greater.

EXAMPLE 3

With the exception of using 23.0 g of caustic soda and 8.6 g of sodiumnitrate, the same method as the example 1 was used to heat and melt 20 gof the platinum group element-containing material comprising palladiumselenide as the primary component, and then subject this melt to waterleaching and filtering. The leaching rate of selenium into the filtratewas 97.2%. Platinum and palladium were not detected in the filtrate.Furthermore, the proportion of hexavalent selenium in the filtrate wasless than 10%. Meanwhile, when the filtered precipitate was repulpedwith 3N hydrochloric acid, and then oxidized with hydrogen peroxide, theleaching rate of palladium into the solution was 95%, and the leachingrate for platinum was 99% or greater.

EXAMPLE 4

Following repulping of 5 kg of decoppered electrolysis slime in 5 L ofhydrochloric acid and 2 L of water, hydrogen peroxide was addedgradually to the mixture, and the temperature of the liquid wasmaintained at 70° C. to effect oxidizing leaching. Following cooling,the chlorination leaching residue was filtered, the acid concentrationof the filtrate was adjusted, and the filtrate was mixed with 1.5 L ofdibutyl carbitol, thus extracting the gold into the dibutyl carbitol.The respective concentration levels within the post-extraction liquidwere 30 mg/L for gold, 58.9 g/L for selenium, 15 mg/L for platinum, and172 mg/L for palladium. Sulfur dioxide gas was bubbled through thisliquid to reduce the selenium at a liquid temperature of 80° C., andfollowing cooling, the liquid was filtered. 901 g of this seleniumprecipitate was distilled in the atmosphere at 750° C. to separate theselenium, and when the 6.9 g of distillation residue was recovered andassayed, it was found to contain 45.2% of palladium, 4.2% of platinum,15.3% of gold, and 34.2% of selenium. 5.7 g of caustic soda and 3.0 g ofsodium nitrate were added to this distillation residue, and the samemethod as the example 1 was then used to heat and melt the mixture, andthen subject this melt to water leaching and filtering. The leachingrate of selenium into the filtrate was 98.4%. Platinum and palladiumwere not detected in the filtrate. Furthermore, the proportion ofhexavalent selenium in the filtrate was less than 10%. Meanwhile, whenthe filtered precipitate was repulped with 3N hydrochloric acid, andthen oxidized with hydrogen peroxide, the leaching rate of palladiuminto the solution was 95%, and the leaching rate for platinum was 99% orgreater.

COMPARATIVE EXAMPLE 1

With the exception of replacing the mixture of caustic soda and sodiumnitrate with 27 g of only caustic soda, the same method as the example 1was used to heat and melt the platinum group element-containing materialcomprising palladium selenide as the primary component, and then subjectthis melt to water leaching and filtering. The leaching rate of seleniuminto the filtrate was 33.6%, much lower than the value observed in theexample 1. Platinum and palladium were not detected in the filtrate.Furthermore, the quantity of hexavalent selenium in the filtrate wasless than 10%. Meanwhile, when the filtered residue was repulped with 3Nhydrochloric acid, and then oxidized with hydrogen peroxide, theleaching rate of palladium into the solution was 95%, and the leachingrate for platinum was 99% or greater.

COMPARATIVE EXAMPLE 2

With the exception of replacing the mixture of caustic soda and sodiumnitrate with 57.6 g of only sodium nitrate, the same method as theexample 1 was used to heat and melt the platinum groupelement-containing material comprising palladium selenide as the primarycomponent, and then subject this melt to water leaching and filtering.The leaching rate of selenium into the filtrate was 98.5%. Platinum andpalladium were not detected in the filtrate. However, the quantity ofhexavalent selenium in the filtrate was 25%, much higher than the valueobserved in the example 1. Meanwhile, when the filtered residue wasrepulped with 3N hydrochloric acid, and then oxidized with hydrogenperoxide, the leaching rate of palladium into the solution was 95%, andthe leaching rate for platinum was 99% or greater.

EXAMPLE 5

When 1 kg of a material containing selenium and platinum group elements(Se: 65%, Te: 30%, Pd: 5%, Pt: 0.5%, Rh: 0.2%, and Ru: 0.4%) was mixedwith 10 L of a 5 mol/L caustic soda solution, and then heated to 80° C.and held at that temperature for 1 hour, the majority of the materialdissolved, yielding a dark purple colored liquid. The liquid was cooledand filtered, and 65 g of residue was recovered. Analysis of thisresidue revealed the platinum group elements Pd, Pt, Rh and Ru as theprimary components, and the assay results were Pd: 80%, Pt: 8%, Rh: 3%,and Ru: 6%. The filtrate was a solution containing Se: 65 g/L and Te: 30g/L, although no platinum group elements were detected.

EXAMPLE 6

When 1 kg of a material containing selenium and platinum group elements(Se: 65%, Te: 30%, Pd: 5%, Pt: 0.5%, Rh: 0.2%, and Ru: 0.4%) was mixedwith 10 L of a 5 mol/L caustic soda solution, and then heated to 80° C.and held at that temperature for 1 hour, the majority of the materialdissolved, yielding a dark purple colored liquid. The liquid was cooledand filtered, and 65 g of residue was recovered. The filtrate was asolution containing Se: 65 g/L and Te: 30 g/L, although no platinumgroup elements were detected. Analysis of the residue revealed theplatinum group elements Pd, Pt, Rh and Ru as the primary components, andthe assay results were Pd: 80%, Pt: 8%, Rh: 3%, Ru: 6%. This residue wasrepulped in 400 ml of hydrochloric acid and 100 ml of water, and withthe liquid temperature held at 70° C., 120 ml of hydrogen peroxide wasadded gradually. Following completion of the hydrogen peroxide addition,the liquid was cooled and filtered, and when the filtrate was analyzed,it was found to contain Pd: 74 g/L, Pt: 7 g/L, Rh: 2.8 g/L, and Ru: 5.5g/L.

EXAMPLE 7

With the exceptions of altering the concentration of the caustic sodasolution to 1 mol/L, and extending the heating retention time to 5hours, alkali leaching was conducted in the same manner as the example5. As a result, 75 g of residue was recovered. The primary componentswithin the residue were Pd, Pt, Rh and Ru, and the assay results werePd: 67%, Pt: 7%, Rh: 3%, and Ru: 5%. The filtrate was a solutioncontaining Se: 63 g/L and Te: 28 g/L, although no platinum groupelements were detected.

EXAMPLE 8

With the exceptions of altering the concentration of the caustic sodasolution to 8 mol/L, and setting the heating temperature to 60° C.,alkali leaching was conducted in the same manner as the example 5. As aresult, 65 g of residue was recovered. The primary components within theresidue were Pd, Pt, Rh and Ru, and the assay results were Pd: 77%, Pt:8%, Rh: 3%, and Ru: 6%. The filtrate was a solution containing Se: 64g/L and Te: 29 g/L, although no platinum group elements were detected.

COMPARATIVE EXAMPLES 3 AND 4

With the exception of altering the concentration of the caustic sodasolution to 0.5 mol/L, alkali leaching was conducted in the same manneras the example 5, but the selenium and tellurium did not dissolve, andthe platinum group elements could not be separated from the selenium andtellurium (comparative example 3).

Furthermore, with the exception of setting the reaction temperature toroom temperature, alkali leaching was conducted in the same manner asthe example 5, but the selenium and tellurium did not dissolve, and theplatinum group elements could not be separated from the selenium andtellurium (comparative example 4).

EXAMPLE 9

600 g of a distillation residue (selenium precipitate distillationresidue; primary component: palladium selenide) of a reductionprecipitate obtained by reduction treatment of the post-gold extractionliquid from a copper electrolysis slime was mixed with 651 g of causticsoda and 345 g of sodium nitrate, and then allowed to react for 2 hoursat 400° C. Following cooling, 15 L of water was added to the crucible,and the resulting mixture was then stirred for 1 hour and filtered,yielding 15 L of filtrate and 348 g of a filtered residue. Theconcentration of Se in the filtrate was 10.4 g/L, indicating a leachingrate of 97.4% for the selenium from the distillation residue. Platinumand palladium were not detected in the leachate. Furthermore, theproportion of hexavalent selenium in the liquid was less than 10%.Analysis of the composition of the filtered residue revealed platinumgroup elements as the primary components, and the respectiveconcentration levels were Pd 44%, Pt 5%, Rh 0.3%, and Ru 1.0%.

Next, when 1 kg of the tellurium precipitate (Se 65%, Te 30%, Pd 5%, Pt0.5%, Rh 0.2%, Ru 0.4%) from the above reduction precipitate was mixedwith 10 L of a caustic soda solution (concentration 5 mol/L), and thenheld at 80° C. for 1 hour, the solution turned a dark purple color. Theliquid was then cooled and filtered, yielding 10 L of filtrate and 65 gof filtered residue. Analysis of the composition of the filteredprecipitate revealed platinum group elements as the primary components,and the respective concentration values were Pd 80%, Pt 8%, Rh 3%, andRu 6%. The Se concentration in the filtrate was 65 g/L and the Teconcentration was 30 g/L, although no platinum group elements weredetected.

Next, the filtered residue was mixed, 3N hydrochloric acid was added andthe mixture was repulped, and then hydrogen peroxide was introduced at70° C. to effect oxidation. The resulting mixture was filtered, and theconcentration levels of the platinum group elements within the resultinghydrochloric acidic solution (filtrate) were Pd 95 g/L (95%), Pt 8.5 g/L(99%), Rh 3.2 g/L (95%), and Ru 0.5 g/L (at least 95%) (wherein thevalues in parentheses are leaching rates).

EXAMPLE 10

With the exception of using 609 g of caustic soda and 432 g of sodiumnitrate, the same method as the example 9 was used to subject 600 g of aselenium distillation residue to heating and alkali melting, and theresulting melt was subsequently subjected to water leaching and thenfiltering. The leaching rate of selenium into the filtrate was 98.2%.Platinum and palladium were not detected in the filtrate. Furthermore,the proportion of hexavalent selenium in the filtrate was less than 10%.Analysis of the composition of the filtered residue revealed platinumgroup elements as the primary components, and the respectiveconcentration were Pd 45%, Pt 5%, Rh 1%, and Ru 2%.

Next, when 1 kg of the tellurium precipitate from the above reductionprecipitate was mixed with 10 L of a caustic soda solution(concentration 5 mol/L), and then held at 80° C. for 1 hour, thesolution turned a dark purple color. The liquid was then cooled andfiltered, yielding 10 L of filtrate and 65 g of filtered residue. The Seconcentration in the filtrate was 65 g/L and the Te concentration was 30g/L, although no platinum group elements were detected. Analysis of thecomposition of the filtered precipitate revealed platinum group elementsas the primary components, and the respective concentration values werePd 80%, Pt 8%, Rh 3%, and Ru 6%.

Next, the filtered residue were mixed, 2 L of hydrochloric acid and 500ml of water were added and the mixture was repulped. With the liquidtemperature maintained at 70° C., 360 ml of hydrogen peroxide was addedgradually to effect oxidation. Following completion of the hydrogenperoxide addition, the mixture was cooled and filtered. Theconcentration of the platinum group elements within the resultingfiltrate were Pd 81 g/L, Pt 7 g/L, Rh 2.1 g/L, and Ru 2.4 g/L.

EXAMPLE 11

The leachate (filtrate) obtained in the alkali leaching of the example 9was held at 80° C., and as the filtrate was neutralized by addingsulfuric acid, a black precipitate began to appear, until the liquidbecome transparent at around pH 7. The precipitate was filtered off andrecovered, and analysis of the composition revealed 68% metallicselenium and 31% metallic tellurium.

EXAMPLE 12

With the exception of using hydrochloric acid instead of sulfuric acid,the example 11 was repeated, and a similar assay of metallic seleniumand metallic tellurium was obtained.

COMPARATIVE EXAMPLE 5

1 kg of a tellurium precipitate was mixed with 1085 g of caustic sodaand 575 g of sodium nitrate, and then allowed to react for 2 hours at400° C., in the same manner as the selenium distillation residue of theexample 9. Following cooling, 25 L of water was added to the crucible,and the resulting mixture was then stirred for 1 hour and filtered, andthe concentrations within the filtrate indicated a leaching rate of 97.4wt % for Se and 98.1% for Te. Platinum and palladium were not detectedin the filtrate. The filtered residue was mixed, 3N hydrochloric acidwas added and the mixture was repulped, and then hydrogen peroxide wasintroduced at 70° C. to effect oxidation. The resulting mixture wasfiltered, and the concentration levels and leaching rates of theplatinum group elements within the resulting hydrochloric acidicsolution (filtrate) were Pd 95 g/L (95%), Pt 8.5 g/L (95%), Rh 1.3 g/L(39%), and Ru 1.5 g/L (14%) (wherein the values in parentheses areleaching rates), indicating a significant decrease in the leaching ratesfor Rh and Ru in comparison with the example 9.

COMPARATIVE EXAMPLE 6

Instead of subjecting the selenium distillation residue from the example9 to alkali melting, 1 kg of the same selenium distillation residue wascombined with 10 L of 5 mol/L caustic soda solution and the temperaturewas maintained at 80° C., but the selenium underwent almost nodissolution.

EXAMPLE 13

When a material containing selenium/tellurium and platinum groupelements (Se 65%, Te 30%, Pd 5%, Pt 0.5%, Rh 0.2%, and Ru 0.4%)comprising 1 kg of a selenium/tellurium reduction precipitate was mixedwith 10 L of a 5 mol/L caustic soda solution and then held at 80° C. toconduct alkali leaching, the majority of the material dissolved,yielding a dark purple colored liquid. The liquid was cooled andfiltered, and 65 g of residue was recovered. The filtrate contained Se:65 g/L and Te: 30 g/L, although no platinum group elements weredetected. With the temperature held at 80° C., sulfuric acid (50%concentration) was added, and when neutralization was continued to pH 7,a black colored powder precipitated. The composition of this precipitatewas Se: 68.5%, Te: 31.5%. Furthermore, the concentrations of Se and Teleft in the filtrate were 530 ppm and 210 ppm respectively. Theprecipitate was introduced into a copper smelting process, electrolyticrefining was conducted, and the anode slime was leached into thesulfuric acidic electrolyte, with air bubbled through the electrolyte.The majority of the Te within the anode slime was dissolved, and the Teassay of the slime following leaching was 0.5%. Furthermore, because Seis not dissolved, no Se was detected in the leachate, and the Se assayof the slime following leaching was 8.3%. The leachate was passedthrough a column packed with copper chip, thus recovering the Te in theliquid as copper telluride. Furthermore, the residual Se and gold in theslime was dissolved by hydrochloric acid oxidizing leaching, andfollowing solvent extraction of the gold, sulfur dioxide was introducedinto the post-extraction liquid to reduce and recover the selenium.Analysis of the composition of the above alkali leaching residuerevealed the platinum group elements Pd, Pt, Rh and Ru as the primarycomponents, and the respective assay values were Pd 80%, Pt 8%, Rh 3%,and Ru 6%. This residue was repulped with 2 L of hydrochloric acid and500 ml of water, and with the liquid temperature maintained at 70° C.,360 ml of hydrogen peroxide was added gradually. Following completion ofthe hydrogen peroxide addition, the mixture was cooled and filtered, andsubsequent analysis of the resulting filtrate revealed concentrationlevels of Pd 81 g/L, Pt 7 g/L, Rh 2.1 g/L, and Ru 2.4 g/L.

EXAMPLE 14

600 g of a distillation residue (Se: 50%, Pd: 40%, Pt: 3%, Rh: 1%, andRu: 2%) obtained by reducing the post-gold extraction liquid from acopper electrolysis slime and then performing distillation treatment wasmixed with 651 g of caustic soda and 345 g of sodium nitrate, and thenallowed to react for 2 hours at 400° C. to effect alkali melting.Following cooling, when 15 L of water was added to the mixture, and theresulting mixture was then stirred for 1 hour and then filtered, 97.4%of the selenium had been leached into the filtrate, whereas platinum andpalladium were not detected. Furthermore, the proportion of hexavalentselenium in the liquid was less than 10%.

EXAMPLE 15

To 1 kg of a tellurium precipitate, obtained by introducing furthersulfur dioxide gas into the liquid remaining following separation of theselenium precipitate in the example 14, was added 10 liters of a 5 mol/Lcaustic soda solution, and when alkali leaching was conducted with thetemperature maintained at 80° C., the majority of the precipitatedissolved, and the solution turned a dark purple color. The liquid wasthen cooled and filtered, yielding a residue of 65 g. Analysis of theresidue revealed the platinum group elements Pd, Pt, Rh and Ru as theprimary components. This residue was repulped in 2 liters ofhydrochloric acid and 500 ml of water, and with the liquid temperatureheld at 70° C., 360 ml of hydrogen peroxide was added gradually.Following completion of the hydrogen peroxide addition, the liquid wascooled and filtered. Analysis of the filtrate revealed Pd 81 g/L, Pt 7g/L, Rh 2.1 g/L, Ru 2.4 g/L, and Au 3.8 g/L. 6.1 g of hydroxylaminehydrochloride was added to the solution as a reducing agent, and themixture was reacted for 1 hour at 60° C. Following cooling, reanalysisof the noble metals in the solution revealed no changes in the dissolvedquantities of Pd, Pt, Rh and Ru, but the quantity of dissolved gold haddecreased to 0.05 g/L, indicating that Au had been selectively reduced.

COMPARATIVE EXAMPLE 7

When the example 15 was repeated and hydrazine was used as the reducingagent, the Pd and Pt was reduced together with Au, meaning Au could notbe separated from the platinum group elements.

INDUSTRIAL APPLICABILITY

A separation process of the present invention enables metals includingthe platinum group elements Pt, Rh, Ir and Ru, as well as selenium,tellurium, gold, silver and copper and the like contained in, forexample, the insoluble residue by-product that forms in the electrolyteduring the copper electrolysis step of a copper smelting and refiningprocess, to be separated and recovered simply, efficiently, and at lowcost.

1. A separation process for platinum group elements comprising: a step(A) for treating a material containing selenium/tellurium and platinumgroup elements with alkali, a step (B) for leaching selenium/tellurium,and a step (C) for separating a platinum group element-containingleaching residue and a selenium/tellurium leachate.
 2. A separationprocess according to claim 1, wherein said step (A) for treating amaterial containing selenium/tellurium and platinum group elements withalkali is a step in which a flux comprising a mixture of caustic sodaand sodium nitrate is added to said material containingselenium/tellurium and platinum group elements, and a resulting mixtureis melted by heating to a temperature exceeding a eutectic temperatureof said flux, said step (B) for leaching selenium/tellurium is a stepfor leaching an obtained melt with water, and said step (C) forseparating said platinum group element-containing leaching residue andsaid selenium/tellurium leachate is a step for conducting a solid-liquidseparation using water leaching, thus separating a mixture into a liquidfraction containing sodium selenite, and a residue containing platinumgroup elements.
 3. A separation process according to claim 2, wherein amolar ratio between said caustic soda and said sodium nitrate is withina range from 75:25 to 85:15.
 4. A separation process according to claim2, wherein hydrogen peroxide and hydrochloric acid are added to saidresidue containing platinum group elements to dissolve said platinumgroup elements.
 5. A separation process according to claim 2, whereinsaid material containing selenium/tellurium and platinum group elementsis an extraction residue process precipitate left after a solventextraction has been used to separate gold from a hydrochloric acidleachate from a decoppered slime.
 6. A separation process according toclaim 2, wherein said material containing selenium/tellurium andplatinum group elements is a distillation residue produced by convertinga decoppered slime to a slurry by adding hydrochloric acid and hydrogenperoxide, filtering said slurry to effect a separation into a leachingresidue containing primarily silver, and a leachate containing gold,platinum group elements, selenium and tellurium, subsequently adjustingliquid characteristics of said leachate and then using a solventextraction to separate gold from said leachate, adding sulfur dioxide toa post-gold extraction liquid to sequentially reduce and precipitate outselenium and then tellurium, and then heating said precipitated materialcontaining platinum group elements and selenium to concentrate theplatinum group elements, while distilling and separating off selenium.7. A separation process according to claim 1, wherein said step (A) fortreating a material containing selenium/tellurium and platinum groupelements with alkali, and said step (B) for leaching selenium/telluriumare conducted simultaneously as an alkali leaching process, in whichsaid material containing selenium/tellurium and platinum group elementsis leached with alkali at high temperature, causing selenium/telluriumto migrate into an alkali liquid, and a solid-liquid separation is thenconducted to separate a resulting mixture into a solid fractioncontaining platinum group elements, and a liquid fraction containingselenium/tellurium.
 8. A separation process according to claim 7,wherein hydrochloric acid and an oxidizing agent are added to aseparated solid fraction generated in said solid-liquid separation, thusdissolving said platinum group elements.
 9. A separation processaccording to claim 7, wherein said material containingselenium/tellurium and platinum group elements is leached with alkali athigh temperature, causing tellurium to migrate into said alkali liquidwith selenium, thus effecting a separation from said platinum groupelements.
 10. A separation process according to claim 7, wherein saidmaterial containing selenium/tellurium and platinum group elements isleached using an alkali concentration of at least 1 mol/L, at atemperature of at least 60° C.
 11. A separation process according toclaim 7, wherein hydrochloric acid and either hydrogen peroxide orchlorine gas are added to said solid fraction from said solid-liquidseparation performed after said alkali leaching, thus dissolving saidplatinum group elements.
 12. A separation process according to claim 7,wherein said platinum group elements comprise one or more of rhodium,ruthenium, palladium and platinum.
 13. A separation process according toclaim 7, wherein said material containing selenium/tellurium andplatinum group elements is an extraction residue process precipitateleft after a solvent extraction has been used to separate gold from ahydrochloric acid leachate from a decoppered slime.
 14. A separationprocess according to claim 7, wherein said material containingselenium/tellurium and platinum group elements is a filtered precipitateoduced by converting a decoppered slime to a slurry by addinghydrochloric acid and hydrogen peroxide, filtering said slurry to effecta separation into a leaching residue containing primarily silver, and aleachate containing gold, platinum group elements, selenium andtellurium, subsequently adjusting liquid characteristics of saidleachate and then using a solvent extraction to separate gold from saidleachate, adding sulfur dioxide to a post-extraction liquid toprecipitate either selenium/tellurium, and then subjecting saidprecipitate to solid-liquid separation.
 15. A separation processaccording to claim 7, comprising: an alkali melt process (i), comprisinga step for adding a flux comprising a mixture of caustic soda and sodiumnitrate to a residue from a distillation treatment of a materialcontaining selenium/tellurium and platinum group elements, and thenheating to a temperature exceeding a melting (eutectic) temperature ofsaid mixture, thus dissolving said selenium/tellurium, as said step (A)for conducting said alkali treatment, a step for conducting waterleaching as said step (B) for leaching selenium/tellurium, and furthercomprising said step (C) for separating said platinum groupelement-containing leaching residue and said selenium/telluriumleachate, and an alkali leaching process (ii), comprising a step forleaching a material containing selenium/tellurium and platinum groupelements with alkali at high temperature as said step (A) for conductingsaid alkali treatment and said step (B) for leaching selenium/tellurium,and further comprising said step (C) for separating said platinum groupelement-containing leaching residue and said selenium/telluriumleachate.
 16. A separation process according to claim 15, wherein asolution containing selenium/tellurium and platinum group elements issubjected to a reduction treatment, and a residue generated bysubjecting a portion of a resulting reduction precipitate todistillation treatment is then subjected to alkali melt treatment, whileremaining reduction precipitate is subjected to alkali leachingtreatment.
 17. A separation process according to claim 15, whereinsulfur dioxide gas is introduced into a post-gold extraction liquid of anoble metal recovery system for copper electrolysis slime to effect areduction treatment, and a residue, generated by subjecting a seleniumthat precipitates first to distillation to effect a separation of highpurity selenium, is subjected to alkali melt treatment, whereas atellurium that precipitates next is subjected to alkali leachingtreatment.
 18. A separation process according to claim 15, wherein aleachate obtained in said water leaching of said alkali melt process isrecycled to said alkali leaching process, and subjected to alkalileaching together with a material containing selenium/tellurium andplatinum group elements.
 19. A separation process according to claim 15,wherein a leachate obtained in said alkali leaching process isneutralized by adding sulfuric acid or hydrochloric acid, thusprecipitating selenium/tellurium.
 20. A separation process according toclaim 15, wherein hydrochloric acid is added to a leaching residuegenerated in said alkali leaching process and said alkali melt processin presence of an oxidizing agent, thus dissolving said platinum groupelements.
 21. A separation process according to claim 1, wherein aselenium/tellurium mixture is obtained from said selenium/telluriumleachate, and said obtained selenium/tellurium mixture is thenintroduced into a copper smelting and refining process to generate analloy of selenium and tellurium with copper, said alloy is subjected tocopper electrolysis to recover electrolytic copper, while accumulatingselenium and tellurium within a copper electrolysis slime, and saidcopper electrolysis slime is then subjected to sulfuric acid oxidizingleaching, thus dissolving and separating tellurium in a leachate fromselenium in a leaching residue.
 22. A separation process according toclaim 7, wherein a selenium/tellurium mixture is obtained by addingsulfuric acid or hydrochloric acid to a selenium/tellurium leachateobtained in said alkali leaching process, thus neutralizing saidleachate and precipitating said selenium/tellurium mixture, and saidobtained selenium/tellurium mixture is then introduced into a copperrefining process to generate an alloy of selenium and tellurium withcopper, said alloy is subjected to copper electrolysis to recoverelectrolytic copper, while accumulating selenium and tellurium within acopper electrolysis slime, and said copper electrolysis slime is thensubjected to sulfuric acid oxidizing leaching, thus dissolving andseparating tellurium in a leachate from selenium in a leaching residue.23. A separation process according to claim 15, wherein aselenium/tellurium mixture is obtained by adding a selenium/telluriumleachate obtained in said alkali melt process to a material containingselenium/tellurium and platinum group elements used in said alkalileaching process, subsequently conducting alkali leaching, and thenadding sulfuric acid or hydrochloric acid to a resulting leachate toneutralize said leachate and precipitate said selenium/telluriummixture, and said obtained selenium/tellurium mixture is then introducedinto a copper smelting and refining process to generate an alloy ofselenium and tellurium with copper, said alloy is subjected to copperelectrolysis to recover electrolytic copper, while accumulating seleniumand tellurium within a copper electrolysis slime, and said copperelectrolysis slime is then subjected to sulfuric acid oxidizingleaching, thus dissolving and separating tellurium in a leachate fromselenium in a leaching residue.
 24. A separation process according toclaim 21, wherein said material containing selenium/tellurium andplatinum group elements is a reduction precipitate produced byintroducing sulfur dioxide gas into a post-gold extraction liquid andconducting a reduction treatment.
 25. A separation process according toclaim 21, wherein following a leaching of tellurium by sulfuric acidoxidizing leaching of said copper electrolysis slime, a resultingleachate is contacted with metallic copper, generating copper telluridewhich is subsequently recovered.
 26. A separation process according toclaim 1, wherein hydrochloric acid is added to said platinum groupelement-containing leaching residue in presence of an oxidizing agent, asolid-liquid separation is conducted, and hydroxylamine hydrochloride isthen added to a resulting filtered platinum group element-containingsolution to selectively reduce and precipitate gold.
 27. A separationprocess according to claim 26, wherein alkali treatment of a materialcontaining selenium/tellurium and platinum group elements is conductedat high temperature.
 28. A separation process according to claim 2,wherein hydrochloric acid is added to said residue containing platinumgroup elements in presence of an oxidizing agent, a solid-liquidseparation is conducted, and hydroxylamine hydrochloride is then addedto a resulting filtered platinum group element-containing solution toselectively reduce and precipitate gold.
 29. A separation processaccording to claim 26, wherein a post-gold extraction liquid of a noblemetal recovery system for copper electrolysis slime is used as amaterial containing selenium/tellurium and platinum group elements, andsulfur dioxide gas is introduced into said post-gold extraction liquidto effect a reduction treatment, and a distillation residue generated bysubjecting a selenium that precipitates first to distillation to effecta separation of high purity selenium is subjected to alkali melttreatment to separate a residue containing platinum group elements,whereas a tellurium that precipitates on further sulfur dioxide gasintroduction into said post-gold extraction liquid is subjected toalkali leaching treatment to separate a residue containing platinumgroup elements, and said residues containing platinum group elements arethen combined and used.